Anticorona suspension clamp



y 14, 1963 H. D. SHORT ANTICIORONA SUSPENSION CLAMP 2 Sheets-Sheet 1Filed Oct. 51, 1966 INVENTOR. H. 0. SHORT WMay/ fl ATTORNEYS May 14,1968 H. D. SHORT ANTICORONA SUSPENSION CLAMP 2 Sheets-Sheet 2 Filed001;. 31, 1966 wwww 6 c F INVENTOR. H. o. s H o R T WWW! FIGS ATTORNEYSUnited States Patent 3,383,459 ANTICORONA SUSPENSION CLAMP HerbertDouglass Short, Newmarket, Ontario, Canada,

assignor to Lacal Industries Limited, Newmarket, Ontario, Canada FiledOct. 31, 1966, Ser. No. 590,611 Claims priority, application Canada,Nov. 1, 1965, 944,230 1 Claim. (Cl. 174-144) ABSTRACT OF THE DISCLOSUREThe invention is a suspension clamp assembly for an electricitytransmitting cable having three integral corona flanges extendingoutwardly of the body, one at each end and one at the centre of thebody. The centre flange terminates in spheroidal formations which extendabove the cable receiving channel and which are adapted to receive a pinfor connecting the unit to an insulator chain.

This invention relates to a high voltage suspension clamp adapted tosupport a single conductor of an electrical transmission line.

Clamps of the general type of this invention are suspended from thelower one of a series of line insulators that depend from a transmissiontower to support single conductors in spaced relation to other singleconductors. Transmission voltages are frequently in the order of 250-500 kv., and the conductor cables mounted therein commonly havediameters in the order of two inches. The method of using clamps to holdthese conductors at the towers is well known.

There are many electrical problems in the operation of transmissionlines but an important one is the phenomenon of corona and coronalosses. Corona is a manifestation of ionization formed in air atbreakdown of the air due to high potential differences. It represents aloss of electrical power from the transmission line and should beeliminated or kept within tolerable limits. At the same time it isdesired to transmit as much power as possible over a given line bykeeping voltage high.

It is well known that one can reduce the effect of corona by reducingthe intensity or concentration of the electric field at the surface ofthe clamp created by the potential of the conductor and/or increasingthe electrostatic capacity of the insulators immediately adjacent to theclamp within which the conductor is mounted, which in turn tends to evenout the voltage distribution across the individual insulators of thestring that connect the clamp to the tower, and hence theirsusceptibility to corona formation.

A common, and generally accepted, method of reducing corona with singleconductor clamps of the type of this invention is the use of coronarings inounted 'by means of appropriate brackets to the side of theconductor clamp with their principal plane substantially parallel to thelongitudinal axis of the conductor in the clamp. These rings can bedesigned as effective corona prevention devices at a given transmissionvoltage. They will increase the capacity, and therefore the coupling ofthe clamp, to the lower insulator in the insulator string that extendsfrom the tower so that the voltage distribution across the lineinsulators is improved, and the corona ignition voltage and R.I.V. levelof the line insulators enhanced. They, in addition, can be designed toprovide a large conducting surface to shield the sharper corners of theclamp whereby to reduce the concentration of electrostatic flux at suchparts, and prevent corona discharge.

The mounting of corona rings, however, is relatively costly and involvesmaintenance problems. The rings must be secured to the clamps by meansof brackets and. under heavy ice and wind loads the rings tend todistort, and the brackets tend to fail. There is, thus, a serviceproblem.

Flashover from line to ground through the tower in the path of theinsulators is also a common fault encountered in transmission linepractice. If the flashover occurs across the porcelain it may damage theporcelain of the insulators. It is good practice to provide flashoverdevices to conduct any such fiashover faults away from the insulatorstrings. Here again, the devices must be separately attached and.involve installation and maintenance costs.

It is an object of this invention to provide a less costly, and moreservice-free corona protection than is afforded by the commonly usedrings.

It is a further object of this invention to provide a less costly andmore service-free fiashover protection device than is afforded by thecommonly used devices.

It has been found that effective corona protection capable of improvingthe coupling of the clamp to the insulator string, and shielding sharpparts of the assembly where there tends to be concentration ofelectrostatic flux can be achieved by means of flanges cast integrallywith the clamp but having their principal planes substantially at rightangles to the longitudinal axis of the clamp and, therefore, theconductor. The construction is cheaper in the first instance becausethere is no mechanical connection of the corona protecting device to theclamp, and there are no service problems of the type encountered withthe separately formed corona rings that must be mounted on the side ofthe clamp.

Generally speaking, a suspension clamp assembly, according to thisinvention, for a single conductor comprises an elongated clamp having alongitudinally extending conducto-r channel formed therein, means forsecuring the conductor in the channel with its longitudinal axis alignedwith the longitudinal axis of the conductor channel, the clamp having atleast one integrally formed corona flange having its planessubstantially at right angles to the longitudinal axis of the conductorchannel. The invention will 'be cleanly understood after reference tothe following detailed specification read in conjunction with thedrawings.

In the drawings:

FIGURE 1 is a perspective illustration of a suspension clamp accordingto this invention;

FIGURE 2 is a sectional view along the line 2-2 of FIGURE 1;

FIGURE 3 is a sectional view along the line 3-3 of FIGURE 1, but showingthe socket tongue in position;

FIGURE 4 is an exploded view of an alternative clamp assembly accordingto this invention;

FIGURE 5 is a longitudinal sectional view of FIGURE 4 but showing theclamp elements in operative position; and

FIGURE 6 is a schematic illustration of a bracket suspended at thebottom of a string of insulators on a transmission line tower.

Referring to the drawings, the numeral 10 generally refers to a singleconductor clamp, according to this invention. It comprises twoco-operating sections 12 and 14 having semi-round jaws that togetherdefine a longitudinally extending conductor channel 16. The clampsections 12 and 14 have bolts 18 that extend therethrough, and that haveco-operating nuts 20 adapted to thread onto their free ends to hold theclamp sections 12 and 14 in clamping arrangement to secure a conductortherein in use.

According to the invention, the clamp sections 12 and 14 have flanges 22and 24 respectively at their ends, the flange sections 22 and 24co-operating to form a rounded corona flange or ring at each end of theclamp assembly with its principal plane at right angles to thelongitudinal axis of the conductor channel 16. The corona flange hasgenerous rounded proportions to increase the surface area whereby tolimit the electrostatic field intensity at the surface of the clampassembly at the operating conditions to a level that eliminates, orreduces to an acceptable limit, corona effect. It is also designed andserves the purpose, reducing the distance between the clamp and theporcelain dielectric of an insulator to which the clamp is connected inuse to increasing the coupling of the clamp assembly to the bottominsulator of the insulator string.

In this latter connection, the numeral 26 refers to a standard sockettongue that joins wit-h the downwardly projecting pin of the lowermostinsulator of an insulator string in use. Tongue 26 is connected to theclamp assembly by means of the pin 28 which threads into the clampsection 12, as illustrated in FIGURE 3. The upper end of the tongue 26is pin-connected to the insulator pin, or ball of the lowest insulatorin the insulator string, but depends from the transmission tower in use.

It will be noted that tongue 26 which connects the clamp assembly to aninsulator is short and is adapted to keep the porcelain of the insulatorclose to the body of the clamp. The corona rings are adapted to extendbeyond the edge of the insulator porcelain so that they, by their heightabove the general body of the clamp, achieve a closer coupling to theinsulator.

The corona rings lying outwardly as they do, from the edge of theinsulator, also function as grading rings; grading rings consistingessentially of a ring, or the like, disposed outwardly and at a higherlevel than the porcelain of the lowest insulator, are often used for thepurpose of conducting a flash-over from the line to the tower and awayfrom the string of insulators. It will be apparent that the integralstructure of the flanges of this invention is Well adapted to gradingrings.

As is well known in the art, one can improve the voltage distributionacross the string of insulators from the conductor in the clamp toground by increasing the capacity of the bottom insulator and clampassembly. To do this, one strives to decrease the distance between themetal of the clamp and the porcelain of the first insulator, i.e.achieve a close coupling. The corona flanges of this invention servethis purpose. They also increase the same capacity by presenting anincreased surface area.

FIGURES 4 and illustrate a further embodiment of the invention where athird corona flange is provided intermediate two end flanges, and wherethe end flanges do not extend on the upper side of a conductor in use.In this embodiment, the suspension clamp assembly comprises an elongatedclamp having a body 40 that co-operates with a saddle 42 to define alongitudinally extending conductor channel 44. The saddle 42 hasupwardly extending minor flanges at its ends and is retained in positionto secure a conductor in the conductor channel with its longitudinalaxis aligned with the longitudinal axis of the conductor channel bymeans of a pair of U-shaped clamps 46 that extend over the saddle 42,through the body 40 and have nuts 48 and lock washers 49 at theirbifurcated ends to maintain the assembly secured. Cleats S0 bolted tothe saddle 42 are provided to maintain the U-shaped clamps 46 inposition. In this case, the socket tongue 52 (similar in design to pin26) that mounts the suspension clamp assembly to an insulator on aninsulator string is connected to the clamp assembly by means of pin 54that passes through the assembly and threads into the shoulder 56. Bolt54 is maintained in position by means of a locking pin 58 that entersinto a channel 60, which in turn communicates with the bearing hole inshoulder 62 of the clamp assembly. Pin 58 has an undulation 64 thereinthat springs over the bolt 54 between shoulders 66 and 68 to prevent itfrom accidentally turning out of its mounting as the straight legthereof enters a through hole in bolt 54. Y

In use, cable is clamped to the clamp assembly and tightened intoposition by tightening the U-clamps 46 whereby the cable can besuspended from the lower insulator of an insulator chain.

It will be noted that the body 40 of the suspension clamp is formed witha corona flange 69 at each of its ends. These flanges extend only on theunderside of the conductor channel.

In addition, in the case of the clamp 4t) a second corona flange "i0 isprovided between the flanges 69. Corona flange 70 terminates at thesockets 56 and 62 which, it will be noted, are designed with aspheroidal shape. These spheroidal shoulders at the extremeties of theflange 70 serve to improve the close coupling of the clamp to theinsulator. The flange, in this particular case, is also specially usefulin shielding against corona discharge from the head of bolt 54. It willalso be noted that the ends of the saddle 12 are slightly flanged androunded. In this case, the connecting socket is also short and adaptedto achieve close coupling to an insulation.

It will be apparent that modifications of this invention other thanthose illustrated are possible. The essence of the invention is theelimination of the old separately formed corona rings that were mountedwith their planes parallel to the longitudinal axis of the conductorchannel of the clamp by the provision of a corona flange that is castintegrally with the clamp members and that has its planes at rightangles to the conductor channel. The integrally cast corona rings ofthis invention function electrically in a similar manner to those of theprior art to improve coupling and provide shielding. It is their noveldisposition which permits them to be integrally formed with the clamp.The invention results in very substantial savings in initial costbecause the casting of an integral flange is very much less than thecost of providing a separate appliance and attaching it by means ofbrackets. Moreover, from a maintenance point of view, the invention isto be much preferred over prior practice because it substantiallyeliminates maintenance of the corona rings.

To refer the use of the clamp, reference will be made to schematicillustration of FIGURE 6 where insulators are indicated as capacitorsand the tower is indicated as ground. The clamp is suspended from theinsulator pin of the bottom insulator 102 of a string of insulators 102,104, 106 and 108 that is, in turn, suspended from the transmission tower110. In this connection, the insulators are of standard construction andconsist essentially of a metal cap and a pin separated by a porcelaininsulator. The cap on the top is adapted to receive the pin of acompanion and similar insulator. Such insulators can be consideredelectrically as a capacitor, the metal cap socket being one plate, theporcelain element being the electrolyte, and the pin being the otherplate. Insulators are, in practice, connected in series, the pin of oneinsulator connecting in socket of the cap of the next insulator. Asindicated above, the clamp of this invention connects with the pin ofthe lowermost insulator in a string that depends from the tower.

It is well known that the voltage distribution across a string ofinsulators depending from a tower with a transmission line secured to aclamp assembly that depends from the lowermost insulator is uneven. Itis not uncommon to have as high as 30% of the voltage between the line112 and the tower 110 across the insulator closest to the line with aslittle as 3% of the total voltage across the insulator closest to thetower. Transmission line voltages are commonly in the order of 200-500kv.

It is also known that one can, in effect, increase the combined capacityof the insulator closest to the line and the line clamp by closecoupling the line clamp and the lowermost insulator, i.e., putting theclamp and its conductor closer to the porcelain of the insulator that isclosest to the line. The combined. capacity of the lowermost insulatorand line clamp and line can also be increased by increasing the surfacearea of the line clamp. These effects are achieved with conventionalcorona rings. Both of these effects are also achieved with the novel andeconomical structure of this invention.

The rounded flanges, which increase the surface area of the clamp atcritical points and achieve a closer coupling of the clamp to theinsulator also have the effect of shielding sharp edges of the clamp,and thereby reducing the electrostatic shield intensity of the clamp. Itis well recognized that electrostatic field intensity is very high atsharp edges such as at bolts and corners. By providing a rounded sectionat the flanges, this can be reduced to provide shielding.

The increasing of the combined capacity of the lower insulator and clamphas the effect of achieving a more even voltage distribution across thevarious insulators in a string and reduces the corona inception voltageat which the transmission line may be operated. The shielding effectachieved has a similar result.

What I claim as my invention is:

1. A suspension clamp assembly for connecting a conductor to the bottominsulator of a string of insulators comprising, a body, a saddle adaptedto overlie said body, said saddle and said body cooperating to define aconductor channel, clamp means for clamping a conductor between saidsaddle and said body, said body having three corona flanges extendingtherefrom with their principal planes substantially at right angles tothe longitudinal axis of said conductor channel, the first one of saidthree corona flanges being located at one end of said body, the secondone of said three corona flanges being located at the other end of saidbody, the third one of said corona flanges being located between saidfirst and second corona flanges, each of said corona flanges extendingoutwardly of said clamp means whereby to eifectively shield said clampmeans, said third corona flange terminating on each side of said body ina shoulder having a spheroidal shape at a height above said conductorchannel, and means between the shoulders for connecting said suspensionclamp assembly to said bottom insulator.

References Cited UNITED STATES PATENTS 1,170,725 2/1916 Austin 174-1441,630,423 5/1927 Gothberg 174-169 X 1,799,114 3/1931 Miller 248632,000,652 5/1935 Snyder 174-169 2,122,988 7/1938 Nelson 24858 X2,699,462 1/1955 Exner 174-40 X 3,218,009 11/1965 McWhierter.

LARAMIE E. ASKIN, Primary Examiner.

